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what router platform are you specifying in the net file? That will determin the slot layouts.

I'm guessing here, but being a switch guy did you specify the "ip defaut-gateway" command on the routers you're using as hosts? If you did you will need to turn off IP routing on those routers with the "no ip routing" command. If you didn't you need to add a default gateway to your Host A and Host B routers. You can do it with the "ip route 0.0.0.0 0.0.0.0 <next hop ip address>" command or the "ip default-gateway" command if you turn off ip routing